This invention relates to an advanced water treatment technique for oxidative destruction of harmful substances typified by environmental hormones, such as dioxins and PCB, by using the strong oxidation power of ozone.
Today, we face the growing problem of how to deal with harmful substances, such as environmental hormones, on the earth. Dioxins are typical examples of harmful substances. It is reported that dioxins generated in Japan (those generated by incinerator plants of its municipalities alone) amount to 2,800 grams (fiscal 1998). To cope with this problem, controls of incinerator plants, sources of generation of dioxins, are being made stricter so as to limit the amounts of dioxins generated thereat.
However, restrictions alone on the generation of dioxins is not sufficient for reduction of the amount of dioxins present in the environment, because once they are generated, they circulate through the environment without being destroyed. Therefore, unless dioxins circulating in the environment are destroyed to thereby end their circulation while the amount of generation thereof is restricted, the whole amount of dioxins in nature cannot be decreased.
For instance, dioxins circulate in the environment as follows: Dioxins once released from an incinerator plant contaminate food, such as agricultural, livestock and fishery products, enter human bodies via the food, and then are discharged as wastes from human bodies into the environment. Those wastes containing harmful substances, such as dioxins, are collected in human wastes treatment facilities and public sewage works, or put together in single or joint private sewage systems all over the country and flow therefrom into rivers and then into the sea.
As described above, dioxins collected in human wastes treatment facilities or public sewage works via human wastes are released into the environment without being decomposed. Harmful substances released into the environment repeatedly return to human bodies via fishery products and the like while being increased in concentration. As described hereinabove, unless the vicious circle in the circulation of dioxins is broken anywhere, adverse influences of dioxins present in the environment on human bodies cannot be reduced even if only the amount of generation of dioxins is restricted.
The ozone treatment and the hydrogen peroxide solution treatment are known as techniques of decomposing harmful substances present in water to be treated. According to these treatments, it is true that harmful substances were subjected to oxidative destruction to some purpose, but almost all of these techniques only mix ozone and hydrogen peroxide solution with water to be treated, or simply agitate the resulting mixture. Therefore, it cannot be necessarily said that they are capable of fully achieving the effects of destroying harmful substances. Even now, harmful substances, including dioxins, continue to increase in water systems in the environment, and hence the advent of a new advanced water treatment technique has been desired which promises more excellent treatment effects.
The present invention has been made in order to meet the above-described demand. That is, an object of the present invention is to provide an advanced water treatment technique that does not simply make use of ozone, differently from the conventional water treatment technique, but is based on an ozone treatment which is capable of braking a vicious circle of harmful substances, such as dioxins, through wastes discharged from human bodies, by providing more advanced treatment effects.
To attain the above object, the advanced water treatment process according to the present invention is based on an essential treatment process for bringing minute bubbles of ozone having an average particle diameter (bubble diameter) of e.g. 0.5 to 3 xcexcm into contact with water to be treated, which contains harmful substances, such as dioxins and PCB, thereby carrying out the ozone treatment for oxidative destruction of the harmful substances contained in the water. In a more concrete form, an advanced water treatment system of the present invention is characterized by comprising an ozone treatment device for bringing minute bubbles of ozone having an average particle diameter (bubble diameter) of e.g. 0.5 to 3 xcexcm into contact with the water to be treated, in a retentive manner, thereby carrying out oxidative destruction of the harmful substances.
According to this advanced water treatment process and system, ozone is not simply supplied to the water to be treated but minute bubbles of ozone are supplied to the water to be treated. More specifically, each minute bubble of ozone has a very small buoyant force, and hence ozone can be caused to stay within the water for a much longer time period. Further, areas of ozone brought into contact with the water can be made by far the larger. As a result, differently from the conventional water treatment process in which aeration is simply carried out with ozone, the efficiency of oxidation of harmful substances dissolved in the water can be dramatically improved.
The xe2x80x9cwater to be treatedxe2x80x9d for treatment by the advanced water treatment process and system of the present invention includes water at high pollution levels, such as waste water containing sludge and soil, human excreta, sewage water containing excreta of domestic animals, household waste water, clinical waste water, papermaking waste water, and industrial liquid waste, and water at low pollution levels, such as water in rivers or lakes, water used in bathhouses, swimming pools, and the like. In short, since the treatment is intended for decomposing harmful substance, so long as the water to be treated contains harmful substances, the kind of a pollution source does not matter.
Further, the harmful substances which can be decomposed include dioxins, PCB, and other environmental hormones. It goes without saying that the present process and system is capable of sterilizing infective disease such as Escherichia coli, salmonella, and mad cow disease.
Further, the advanced water treatment system may be of a fixed type, or an in-vehicle mobile type, but is characterized by the capability of continuous treatment.
As described hereinabove, the ozone in the form of minute bubbles has a very small buoyant force and stays within the water for a very long time period. Therefore, there is a difficulty that if only the minute bubbles of ozone are simply supplied to the ozone treatment tank, it takes much time for the ozone to be uniformly diffused throughout the water within the tank, and hence the high oxidative destruction power of the ozone realized in the form of minute bubbles is not fully made use of. Therefore, in the water treatment process of the present invention, as one method of evenly diffusing the minute bubbles of ozone, the minute bubbles are supplied to a water pipe which is provided for connecting each treatment tank arranged within a treatment system. The water is flowing violently through the water pipe, so that ozone formed into minute bubbles by xe2x80x9cozone supply meansxe2x80x9d comprised of an ozone generator and an ozone bubble-forming device (line mixer type, or vortex flow turbine pump type) is supplied to the water flowing through the water pipe, whereby the minute bubbles of ozone are injected into the ozone treatment tank in a gushing flow and evenly diffused throughout the inside of the tank.
Further, in another method of diffusing the minute bubbles of ozone, an ozone treatment tank for bringing the minute bubble of ozone into contact with the water to be treated in a retentive manner is provided within the treatment system, and the ozone is blown from the bottom of the tank into the water within the tank to cause a forced convection of the water. In other word, an ozone treatment tank for bringing the minute bubbles of ozone into contact with the water to be treated in a retentive manner is provided within the treatment system, and the water within the tank and the minute bubbles of ozone supplied from the ozone generator are vigorously moved around to produce a forced convection state of the water. An ozone treatment device using the ozone bubble-forming device (rotational type) arranged at the bottom of the ozone treatment tank carries out the ozone treatment. In this case, the water to be treated and ozone are vigorously turned around to blow minute bubbles of ozone having an average particle size of 10 to 20 xcexcm, or 50 to 60 xcexcm, into the water in the tank.
Further, the advanced water treatment process and device may use one ozone treatment tank, but if a plurality of ozone treatment tanks are arranged at successive respective stages, they can provide enhanced oxidative destruction effects. Further, when the plurality of ozone treatment tanks are provided, the tanks should not be simply arranged at respective successive stages, but it is preferred that extra ozone coming up from the water within the latter-stage ozone treatment tank is caused to be circulated to the former-stage ozone treatment tank for effective utilization of ozone.
Further, the advanced water treatment process and system is capable of performing oxidative destruction of almost all harmful substances in the water to be treated, by utilizing the minute bubbles of ozone. However, the present invention further performs a desired combination of a hydrogen peroxide solution treatment, an electrolysis treatment, an ultraviolet radiation treatment, and a carbonized filter medium contract treatment (carbonized filter medium treatment) to thereby more effectively decompose the harmful substances.
One combination-type treatment provides an example suitable for advanced treatment of waste water at relatively low pollution levels, including water from waterworks, swimming pools, and bathhouses, and water in rivers. In this example, the advanced water treatment process and system is configured such that the ozone treatment, the ultraviolet radiation treatment, and the carbonized filter medium contact treatment are carried out in the mentioned order. It should be noted that the ultraviolet radiation treatment decomposes harmful chlorides by dechlorination reaction through irradiation of ultraviolet rays. The carbonized filter medium treatment eliminates harmful substances remaining untreated within the water by adsorbing them by a special filter medium.
The waste water to be treated here has a relatively low pollution load, and hence the ozone treatment can decompose almost all harmful substances, but harmful substances which remain even after the ozone treatment are treated or processed by the ultraviolet radiation treatment. Then, the water to be subjected to the ultraviolet radiation treatment contains ozone in the form of minute bubbles mixed therein by the ozone treatment at the preceding stage, and hence hydroxyl radical (OHxe2x88x92) having a high oxidative power can be generated in a larger amount to provide high decomposition effects. Then, by carrying out the carbonized filter medium contact treatment thereafter, heavy metals, such as aluminum, arsenic, and cadmium, contained in the water to be treated are adsorbed for elimination from the water. As the carbonized filter for use in the treatment, the use of a conifer carbonized filter material obtained by carbonizing raw materials of a plurality of kinds of conifer, including cedar, pine, and Japanese cypress (hinoki) at a high temperature range of 800 to 900xc2x0 C. enhances absorptive action of the medium to a very high degree. By subjecting the water to the above-mentioned sequence of treatments, it is possible to obtain water which is purified to a quality level suitable for drinking water. Further, this treatment process and system can attain sufficient treatment effects by relatively simple treatment, and the costs therefor can be held at a low level.
Another combination-type treatment provides an example suitable for advanced treatment of waste water having a relatively high pollution load, such as human excreta, sewage water, and waste water from agricultural community. In this example, the advanced water treatment process and system is configured such that the hydrogen peroxide solution treatment, the ozone treatment, the ultraviolet radiation treatment, and the carbonized filter medium contact treatment are carried out in the mentioned order. It should be noted that the hydrogen peroxide solution treatment admixes the hydrogen peroxide solution as a liquid in the water to be treated, whereby microorganisms are sterilized and the harmful substances are oxidized, by the oxidative power of the hydrogen peroxide solution.
The waste water treated in this example have relative high pollution loads, and are required to treat human excreta. Therefore, the hydrogen peroxide solution treatment for processing foul odor and human excreta residue is carried out prior to the ozone treatment. In this case, it is advantageous that the foul-odor air generated from the water to be treated within the treatment system is mixed into the hydrogen peroxide solution as minute bubbles having an average particle diameter of approximately 0.01 to 0.2 mm, for oxidative destruction thereof. By forming the foul-odor air into the minute bubbles, the oxidative destruction thereof by the hydrogen peroxide can be carried out with high efficiency. In respect of high-efficiency treatment, it is more advantageous that pH of the water to be treated is adjusted to 8 to 10 in advance, and still further advantageous that at least one of gold, copper oxide, and iron oxide is thrown into the water, for promotion of the oxidative treatment by the hydrogen peroxide. Then, after the hydrogen peroxide solution treatment, the ozone treatment, the ultraviolet radiation treatment, and the carbonized filter medium contact treatment are carried out, whereby the water to be treated can be purified to a quality level suitable for drinking water.
A still another type of the treatment is an example suitable for advanced treatment of waste water containing harmful heavy metals, such as industrial liquid waste from a particular factory, and waste water from a final waste disposal plant. In this example, the advanced water treatment process and system is configured such that the hydrogen peroxide solution treatment, the electrolysis treatment, and the ozone treatment are carried out in the mentioned order. It should be noted that the electrolysis treatment is one which is executed for eliminating heavy metals, such as arsenic, cyanogen, aluminum, cadmium, and the like, which cannot be decomposed by oxidative treatment or dechlorination treatment.
Since the waste water treated here contains heavy metals, the above-mentioned hydrogen peroxide solution treatment is carried out, and then the electrolysis treatment is carried out. This enables the electrolysis treatment to be carried out with high efficiency owing to hydrogen peroxide solution remaining within the water subjected to the hydrogen peroxide solution treatment. After the heavy metals are thus eliminated, the above-mentioned ozone treatment is carried out whereby the water to be treated can be purified to a quality level suitable for drinking water.
As the tank for carrying out the ultraviolet radiation treatment, it is advantageous that an ultraviolet radiation treatment tank is provided which has an ultraviolet light source and inner walls coated with titanium dioxide, and it is further advantageous to carry out a photocatalytic treatment by irradiating ultraviolet rays to the inner walls to consume the foul odor in combination with the ultraviolet radiation treatment. This can more efficiently enhance the efficiency of decomposing the harmful substances by hydroxyl radical. The ultraviolet radiation treatment tank can be configured such that it has a plurality of partition walls coated with titanium dioxide, with partition walls being arranged such that the distance between adjacent ones of the partition walls is within 30 cm. More specifically, the ultraviolet radiation treatment tank has a body in the form of a bottomed hollow cylinder extending vertically, an ultraviolet lamp being arranged in a diametrical center of the body, with the plurality of partition walls having plate surfaces radially extending toward the ultraviolet lamp positioned in the center of the arrangement of partition walls. This enables the electrons causing photocatalytic action to be dispersed evenly throughout the inside of the treatment tank, whereby the photocatalytic effects can be fully provided.
Although each of the above-mentioned types is composed of a sequence of treatments, this is not limitative, but it goes without saying the for each treatment stage, a settling tank may be provided for carrying out the settling treatment, to thereby eliminate impurities contained in the water to be treated.
Further, an aeration treatment may be carried out for a biological treatment of organic contaminants contained in the water to be treated.
In all of the above-mentioned cases, treated water obtained by the advanced water treatment process and system ensures a water quality at a level higher than a level satisfying 26 drinking water-suited water quality criteria defined by the Japanese food sanitation law.